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The panty-selling business isn't anything new, and if you hadn't heard of it before - you may have caught it on Netflix series Orange is the New Black.

In the third series of the award-winning comedy-drama, main character and prison inmate Piper Chapman recruits a string of fellow female felons to wear underpants for a day or two, and smuggle them out of prison to be sold for a pretty profit.

The narrative sees the inmates make a few dollars for going about their daily business, but instead of throwing their undies in the laundry basket with the towels and bedsheets - they get packaged and sent to men on the outside who get off on their used undergarments.

The interest into the fetish went viral, and for the few sites around the world that make money off the dirty business - the episode couldn't have come at a better time. Photo / YouTube

While the concept did raise a few eyebrows and even sicken a few viewers, panty-selling convicts paved the way for a surge in the online "used-underwear" trade.

When the first episode about Piper's business hit our screens in June 2015, Google trends showed the search term "sell used panties" experienced the biggest global spike ever.

The interest into the fetish went viral, and for the few sites around the world that make money off the dirty business - the episode couldn't have come at a better time.

A gap in the market

Alex and his undisclosed business partner, who launched the site SofiaGray.com in 2015, said while they saw a gap in the market for people wanting to buy used underwear for sexual pleasure - their site soared after the airing of the Netflix series.

"The storyline did send a surge of traffic to our site during the months it aired," Alex, who didn't want his surname disclosed, told news.com.au.

"We have no idea who the buyers are, nor do we want to know. We keep all buyers completely anonymous."

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While Alex admits the influence of the OITNB series did wean off, his site is still booming - with one woman this week making a staggering $AU6500 for a single pair of used undies.

"The seller is a student and this is her side income," he said.

"She's a popular seller on the site who has a few dedicated buyers. One of these buyers requested a pair of underwear with "special requirements", all of which were at a price.

"A few figures were thrown around by the buyer, when the seller jokingly quoted $5000, to which the buyer quickly obliged and bought for this amount."

Alex, who says he has a few hundred sellers using his site daily to make money, admits the interest in the fetish creates a profitable second income for women who want to take part.

"Some sellers have supplemented this to be their side income and some have made this their full time job," Alex revealed.

"It really depends on how much you put in. If you're a seller that is consistently listing [new undies] and promoting these items you could see hundreds if not thousands in a month."

Sellers can create a shop on the website, completely free of charge and then list their used undergarments. From here, buyers can browse through the listed items and purchase said items paying via credit and debit cards.

"Buyers purchase as they would with any online transaction via credit and debit cards," he said.

"In the last year it has grown a lot in popularity, because anyone in the world can sell and buy."

People interested in buying used panties on Sofia Gray can browse through different listings and literally "add to cart".

For most of the items up for sale, the price tag lingers around $45 per piece, while others soar into the hundreds.

In Japan, the trade of used underwear is slightly more publicly accepted.

For about $AU6.50, people can purchase a pair of panties manufactured to appear used - straight from a vending machine.

While the Japanese text on the machines makes the fact they "appear" used clear enough, English words such as "used" are prominently featured to attract attention.

Japanese customers instantly know the difference, while foreigners who can't read the language return home with lurid but false tales.

Founded in 2015, Sofia Gray claims to be the largest and safest marketplace for the buying and selling of used underwear, isn't the only sale site.

Pantydeal is another American website which runs on the same business model, but ask for a membership fee from all sellers.

One user, who didn't want to be named, told The New York Post she started selling on their site after working as a waitress and injuring her shoulder, meaning she couldn't work the hours she used to.

"I had to give up my waitress jobs (at the Cheesecake Factory and California Pizza Kitchen) because I could no longer hold the trays. Another server confided that she occasionally sold her underwear for cash. I was intrigued," she said.

"My first deal went like a dream. A guy messaged me about a pair of panties he'd seen on my page. He wanted me to wear them for 24 hours, and to not masturbate in them (most men actually want you to do that). He paid me via PayPal within 20 minutes, and I shipped the undies off in a Ziploc bag and a discreet brown envelope.